Bobbin selectable to vary lower thread tension

ABSTRACT

A bobbin for a lock stitch sewing machine is disclosed having on one flange an annular protuberance concentric with the center of rotation of the bobbin and having on opposite sides of said one flange a pair of annular friction surfaces between which friction surfaces a normal force may be applied to generate friction resistant to rotation of said bobbin, one of said annular friction surfaces being carried on the said raised annular protuberance and the other of said annular friction surfaces extending radially outward beyond the radius of the other of said pair of bobbin flanges. A set of bobbins each having the raised annular protuberance at differing radii may be utilized individually in a lockstitch sewing machine to provide the exact degree of bobbin thread tension required when utilized in a bobbin case wherein bobbin thread tension is achieved by resisting bobbin rotation by pressing a hold down arm against the raised annular protuberance.

United States Patent 1191 Davidson et al.

[ BOBBIN SELECTABLE TO VARY LOWER THREAD TENSION [75] Inventors: Donald R. Davidson, Parsippany;

Edmund B. Wilson, III, Dover, both 21 Appl. No.: 280,021

Related US. Application Data [62] Division of Ser. No. 163,840, July 19, 1971, Pat. No.

[52] US. Cl. 242/118.4, 242/156 [51] Int. Cl B65h 75/14 [58] Field of Search 242/118.4, 118.7, 156,

[56] References Cited UNITED STATES PATENTS 2,190,085 2/1940 Scholl 242/1l8.7 2,643,830 6/1953 Paeplow et al. 242/1 18.61 3,173,625 3/1965 Creter et al..... 242/118.62 3,175,783 3/1965 Ketterer 242/156 X 3,294,341 12/1966 Dolen et a1. 242/118.7 X

3,323,743 6/1967 Landgraf 242/74 3,430,886 3/1969 Sweeney 242/118.7

3,462,097 8/1969 Wilson 242/ll8.7 3,584,819 6/1971 Brough 242/11s.7

[111 3,861,617 1 51 Jan. 21, 1975 Primary Examiner-George F. Mautz Attorney, Agent, or FirmMarshall .1. Breen; Chester A. Williams, Jr.; Robert E. Smith [57] ABSTRACT A bobbin for a lock stitch sewing machine is disclosed having on one flange an annular protuberance concentric with the center of rotation of the bobbin and having on opposite sides of said one flange a pair of annular friction surfaces between which friction surfaces 21 normal force may be applied to generate friction resistant to rotation of said bobbin, one of said annular friction surfaces being carried on the said raised annular protuberance and the other of said annular friction surfaces extending radially outward beyond the radius of the other of said pair of bobbin flanges.

A set of bobbins each having the raised annular 1 Claim, 5 Drawing Figures PATENIHJJMQIGIS 3,861,617

INCREASING BOBBIN THREAD TENSION MEAN DIAMETER 0F RING BOBBIN SELECTABLE T VARY LOWER THREAD TENSION This application is a division of application Ser. No. 163,840, filed July 19, 1971, now US. Pat. No. 3,702,102.

SUMMARY OF THE INVENTION This invention relates to a method of obtaining bobbin thread tension which will enable a sewer to readily select the most appropriate bobbin thread tension for the sewing operation to be performed Diverse sewing operations, such as zigzag sewing of sheer fabrics without pucker, to sewing with elastomer bobbin thread at maximum tension to obtain the maximum shirring effect can be accomplished on one machine by utilizing the apparatus of this invention.

It is known to provide for lower thread tension of the sewing machine by restricting the rotation of the bobbin. This is accomplished by utilizing various forms of spring members such as Bellville washers, leaf springs and coil springs alone or in combination with other members to bear against the rotating bobbin with a pressure sufficient to limit its ready rotation and thereby to apply some tension to removal of the lower thread. It is also generally known to provide means in conjunction with the spring members to provide some adjustability for the bobbin thread tension. These generally only provide for limited degrees of adjustability or are so difficult to calibrate as to place their use beyond the capabilities of the greater majority of home sewers. What is lacking in the prior art is a bobbin thread tension selecting means which may be readily accomplished even by an inexperienced sewer. It is, therefore, an object of this invention to provide a means for readily selecting bobbin thread tension.

It is a further object of this invention to provide a means for readily selecting bobbin thread tension which may be readily and accurately reproduced.

It is a still further object of this invention to provide for that selectable bobbin thread tension which will be optimum for particular sewing operations to be performed.

Yet another object of the invention is to provide for this selectability of bobbin thread tension in a most economical manner.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a vertical axis rotating hook of a conventional lockstitch sewing machine showing the bobbin and bobbin case of the invention in place therein.

FIG. 2 is an enlarged cross sectional view of the bobbin showing the raised concentric friction ring in solid lines in one location and in dotted lines showing the friction ring in two extreme locations.

FIG. 3 is a vertical cross-sectional view taken substantially along line 33 of FIG. 1,

FIG. 4 is a graph depicting the variation in the bobbin thread tension resulting from a variation in the mean diameter of the friction ring, and

FIG. 5 is a plan view of a bobbin case used in FIG. 1 showing a modification of the invention.

Reference to FIGS. 1 and 3 discloses a vertical axis rotary hook of a lockstitch sewing machine which hook rotates in a counterclockwise direction as viewed in FIG. 1. The hook 10 is formed with a loop seizing beak 11 which when cooperating with a threadcarrying needle will pick up a needle thread loop and cast it about a supply of bobbin thread in a well known manner. On the inner diameter of the hook 10 there is a supporting flange or bearing rib 12 on which is supported a bobbin case denoted generally as 14. The bobbin case 14 is constrained against rotation with the rotary hook 10 by a position finger 15 attached to the sewing machine frame and also by a cushion spring 16 attached by screw 17 to a cushion spring bracket 18. The cushion spring bracket is carried by the sewing machine frame in a fashion which allows lateral shift ofthe bracket 18 over the top of the hook and against the bobbin case under the influence of an eccentric stud 19, thereby to adjust the thread clearances between an abutment 20 on the bobbin case and the position finger 15, and between an abutment 21 and the cushion spring 16 so that the needle loop may be cast about the bobbin case by the loop seizing beak 11.

The bobbin case 14 supports a bobbin 23 on a bobbin receiving flange 24 and prevents sidewise shift of the bobbin by the provision of the inner diameter 25. The bobbin itself is constructed with a smaller diameter lower flange 26 to allow the insertion of the bobbin 23 into the bobbin case and the resting of the lower surface 27 of its upper flange 39 on the flange 24. Fitted into a cavity 28 (FIG. 1) in the bobbin case and pivoted on a pin 29 is a bobbin hold-down lever arm 30. The lever arm 30 has a projection 31 beneath the pivot pin 29 acted on by a leaf spring 32 which is attached to the bobbin case by a screw 33 and nut 34. The leaf spring impinges on an edge of the lever arm projection 31 to impart a moment to the lever arm 30. This moment causes the lower surface 35 of the lever arm to press against a concentric raised annular ring 36 formed on the upper bobbin flange 39. The force exerted by the lower surface 35 of the lever arm against the raised annular ring 36 presses the lower surface 27 of the upper flange 39 against the bobbin receiving flange 24 of the stationary bobbin case and thereby creates frictional resistance to bobbin rotation on two different annular friction surfaces 36 and 27 resulting in bobbin thread tension.

FIG. 2 is a cross-sectional view of the bobbin showing in solid lines a raised annular ring 36 of one diameter concentric about the bobbin center line and also indieating in phantom lines two other raised annular rings 37 and 38, respectively, of maximum diameter 37 and minimum diameter 38. Regardless of the position of the annular friction ring the moment exerted by the leaf spring 32 on the lower surface 35 of the lever arm 30 is a constant value. Utilizing a bobbin with the largest diameter raised annular friction ring 37 will provide the shortest lever arm distance on the lever arm 30 resulting in the greatest force exerted on the bobbin by the lever arm. For a given coefficient of friction between the lever arm 30 and the raised annular ring 37 and between the lower surface 27 of the upper flange of the bobbin and the bobbin receiving flange 24 of the bobbin case there will correspondingly be generated the largest retarding moment to bobbin rotation which will result in large bobbin thread tension.

On the other hand, utilizing a bobbin having the smallest diameter raised annular ring, as indicated by 38, will provide the longest lever arm distance on the lever arm 30, resulting in the least force exerted on the bobbin by the lever arm. The resulting low frictional force on the raised annular ring of the bobbin and on the lower surface of the upper flange of the bobbin when combined with the effect of the small radius of the raised annular ring from the bobbin center will produce a minimum bobbin resistance to rotation or minimum bobbin thread tension.

The effect of the diameter of the raised annular ring on bobbin thread tension is shown in FIG. 4. The increase in bobbin tension is not linear with the increase in the mean diameter of the raised annular ring because there are two radii involved, that of the hold-down arm where it impinges the raised annular ring and that of the raised annular ring itself.

In FIG. 5 is shown a bobbin case having a modification of the invention which may be used on bobbins having no raised annular friction ring thereon. With this modification tension adjustments may be made without changing bobbins. In this view is shown a bobbin case hold-down arm 45 which is supported on a pivot pin 29 and acted upon by a leaf spring 32, as in the construction shown in FIGS. 1, 2 and 3. The holddown arm 45 is formed with scribe marks 46, 47 and 48 at different distances from the pivot pin 29. A friction shoe 49 slidably affixed to the bobbin case hold down arm 45 will provide a rubbing surface between a conventional bobbin and the hold-down arm 45, thereby taking the place of the raised annular rings 36, 37 and 38 previously described. The scribe marks 46, 47 and 48 may be previously calibrated to locate the positions for the friction shoe which will give rise to bobbin thread tension appropriate for zigzag stitching and straight sewing as well as for obtaining shirring effects with elastomeric threads. Making bobbin thread tension adjustment from one type of sewing operation to another simply requires sliding of the friction shoe 49 to the appropriate scribe mark before proceeding with the sewing operation.

Having thus set forth the nature of this invention, what is claimed herein is:

l. A bobbin for use in a lock-stitch sewing machine wherein bobbin thread tension is achieved by frictionally resisting bobbin rotation said bobbin having:

a. a pair of circular flanges between which thread is adapted to be wound.

b. a circular hub on which thread is adapted to be wound separating said flanges, at least a dimetrical cross-sectional portion of said hub between said flanges being solid and concentric to the bobbin axis of rotation and to said flanges.

c. at least one raised annular protuberance formed on one of said pair of flanges concentric to the bobbin axis of rotation,

(1. two different annular friction surfaces formed one on each side of said one of said pair of bobbin flanges between which friction surfaces a normal force may be applied to generate frictional resistance to rotation of said bobbin, one of said annular friction surfaces being carried on said raised annular protuberance and the other of said annular friction surfaces extending radially outward beyond the radius of the other of said pair of bobbin flanges, whereby said other of said annular friction surfaces supports said bobbin for rotation in said lockstitch sewing machine.

l I =l 4 

1. A bobbin for use in a lock-stitch sewing machine wherein bobbin thread tension is achieved by frictionally resisting bobbin rotation said bobbin having: a. a pair of circular flanges between which thread is adapted to be wound, b. a circular hub on which thread is adapted to be wound separating said flanges, at least a dimetrical cross-sectional portion of said hub between said flanges being solid and concentric to the bobbin axis of rotation and to said flanges, c. at least one raised annular protuberance formed on one of said pair of flanges concentric to the bobbin axis of rotation, d. two different annular friction surfaces formed one on each side of said one of said pair of bobbin flanges between which friction surfaces a normal force may be applied to generate frictional resistance to rotation of said bobbin, one of said annular friction surfaces being carried on said raised annular protuberance and the other of said annular friction surfaces extending radially outward beyond the radius of the other of said pair of bobbin flanges, whereby said other of said annular friction surfaces supports said bobbin for rotation in said lockstitch sewing machine. 